This invention relates to a thermal imaging system and in particular a thermal imaging system for monitoring temperature profiles in kilns or furnaces.
When monitoring temperature profiles within a kiln or furnace it is usual to use a thermal imaging camera to produce thermal images and to display these to a user on a suitable display. The images can be displayed in real time or can be processed prior to or during display. Usually the images are displayed on a visual display unit (VDU) of a computer which may be provided with image processing software to process the normal images. In conventional systems of this type, only a single temperature range is capable of being measured by the camera at any one time and thermal images in the specified temperature range are displayed in real time. This can lead to problems because with such systems, the high temperature images are dominant because luminance increases exponentially with temperature and therefore the low temperature images can be masked by the dominant high temperature images and can even be indistinguishable from noise. This means that the dynamic range of such camera is quite small. This is particularly a problem when a silicon CCD camera is used because whilst this camera is able to produce adequate images in the near infrared region, it does suffer from a restricted dynamic range. If the dynamic range is to be increased to give greater resolution of temperatures in the thermal images, and in particular of low temperatures, it is necessary to cool the camera used and also to use very high specification components in the camera and it will be appreciated that this leads to a considerable increase in the cost of manufacture of these cameras and any imaging system incorporating them.
It is an object of the present invention to provide a thermal imaging system in which images taken over multiple temperature ranges can be monitored simultaneously whilst only images from one selected temperature range are displayed to a user. It is a further object of the invention to provide a relatively low cost imaging system in which the dynamic range of the system is increased.
Thus and in accordance with the present invention therefore there is provided a thermal imaging system comprising a camera to produce thermal images of an object and a display device to display thermal images produced by the camera, said camera including shutter means operable to allow exposure of an image for a selected interval, each different selected interval allowing the camera to produce a thermal image over a selected temperature range, wherein said system is operable such that one said selected interval of operation of said shutter is repeated periodically and said display device displays said thermal image produced at said one selected interval.
With this arrangement it is possible for the thermal imaging system to produce on a display a continuous real time display of a thermal image of an object over one selected temperature range whilst also simultaneously allowing monitoring of the thermal image over other temperature ranges.
Preferably the shutter means is an electronic shutter and is operable to allow exposure over selected intervals in the range {fraction (1/50)} to {fraction (1/10,000)} secs.
Preferably the one said selected interval of operation of the shutter is repeated every second shutter operation.
Preferably the system includes a processing device which is adapted to process the thermal image produced by the camera prior to display on the display device. Preferably the processing device includes a user operable control whereby a user can control said processing of the thermal image.
Preferably the display device comprises a computer system and most preferably the computer system includes thermal image processing software. In the latter case, the display device and the processing device are formed as one unit.